Sensor package having a sensor chip

ABSTRACT

Some embodiments herein relate to a sensor package. The sensor package includes a printed circuit board with a laminar current conductor arranged on a first main surface of the printed circuit board. The sensor package also includes a sensor chip adapted to measure a current flowing through the laminar current conductor, wherein the sensor chip comprises a magnetic field sensor. The sensor chip is electrically insulated from the current conductor by the printed circuit board, and is arranged on a second main surface of the printed circuit board opposite to the first main surface. The sensor chip is hermetically sealed between the mold material and the printed circuit board, or is arranged in the printed circuit board and hermetically sealed by the printed circuit board.

TECHNICAL FIELD

Some embodiments of the present disclosure relate to sensor packages andmethods for producing sensor packages, for example sensor packagescomprising magnetic field sensors, which sense the magnetic field of acurrent.

BACKGROUND

Current sensors are used for a variety of applications, for examplecurrent limitation, over-current protection or simply for monitoring theintensity of a current. For such applications, Hall-sensors or similarsensors are widely used. Hall-sensors sense the magnetic field of theCurrent and provide a voltage (Hall voltage) proportional to theintensity of the current. As the magnetic field decreases withincreasing distance between the magnetic field sensor and the current,the semiconductor die comprising the Hall-sensor has to be brought closeto the conductor carrying the current to be measured to have asufficiently strong magnetic field.

U.S. Patent Publication No. 2008/0297138 A1 describes a current sensorwith lead frames forming a current conductor portion and a substratecomprising a magnetic field sensing element arranged above a currentconductor portion provided by the lead frame to measure the currentflowing through the current conductor portion. Also U.S. Pat. No.7,166,807 B2 and U.S. Pat. No. 6,995,315 B2 describe current sensorswith magnetic field sensors based on the lead frame technology asstructural-design technology.

U.S. Pat. No. 5,041,780 describes an integrable current sensor, whereina current conductor is provided on top of a semiconductor substratecomprising the magnetic field sensing elements. A further example of asemiconductor device with a Hall-effect element and a conductor arrangedon top of the semiconductor substrate is described in U.S. Pat. No.6,424,018 B1.

Current sensors based on lead frame structures or semiconductor carriersor ceramic carriers cause high costs with regard to the material andwith regard to the production processing. Furthermore, the current to bemeasured produces eddy currents in neighboring conductors or conductivelayers, for example used as electrostatic shields, wherein the eddycurrents in return produce magnetic fields that superimpose to themagnetic field of the current to be measured, and thus deteriorate thesensitivity and the calibration of the current measurement of thesensor.

German Patent publication DE 10 2006 026 148 A1 describes an electronicdevice comprising a load current path consisting of two conductor tracesarranged on top of each other in a multi-layer printed circuit board andinsulated by the printed circuit board from each other. The devicefurther comprises a Hall-sensor arranged below the printed circuit boardand the two conductor traces for a current measurement of the loadcurrent path. The Hall-sensor is electrically connected to a measurementevaluation unit via conductor traces on the lower surface of the printedcircuit board. Current sensor arrangements as described in German Patentpublication DE 10 2006 026 148 A1 are expensive to produce, expensive totest, only show a limited measurement sensitivity, which additionallydeteriorates over the lifetime of the electronic device.

SUMMARY

The following presents a simplified summary in order to provide a basicunderstanding of some aspects of the invention. This summary is not anextensive overview of the invention, and is neither intended to identifykey or critical elements of the invention nor to delineate the scope ofthe invention. Rather, the purpose of the summary is to present someconcepts in a simplified form as a prelude to the more detaileddescription of different embodiments presented later.

Embodiments of the present invention provide a sensor package,comprising: a printed circuit board with a laminar current conductorarranged on a first main surface of the printed circuit board; a sensorchip adapted to measure a current flowing through the laminar currentconductor, wherein the sensor chip comprises a magnetic field sensor,wherein the sensor chip is electrically insulated from the currentconductor by the printed circuit board, and wherein the sensor chip isarranged on a second main surface of the printed circuit board oppositeto the first main surface and is hermetically sealed between a moldmaterial and the printed circuit board, or wherein the sensorsemiconductor die is arranged in the printed circuit board and ishermetically sealed by the printed circuit board.

Further embodiments of the present invention provide a method forproducing a sensor package, the method comprising: providing a printedcircuit board with a laminar current conductor arranged on a first mainsurface of the printed circuit board; providing a sensor chip adapted tomeasure a current flowing through the laminar current conductor, whereinthe sensor chip comprises a magnetic field sensor; arranging the sensorchip on a second main surface of the printed circuit board opposite tothe first main surface such that the sensor chip is electricallyinsulated by the printed circuit board from the current conductor; andhermetically sealing the sensor chip between a mold material and aprinted circuit board; or arranging a sensor chip in the printed circuitboard such that the sensor chip is electrically insulated by the printedcircuit board from the current conductor and such that the sensor chipis hermetically sealed.

Current sensors for measuring a current based on the magnetic fieldproduced by the current to be measured typically comprise (a) a currentconductor for the current to be measured, (b) a semiconductor die orchip with magnetic field sensors arranged close to the currentconductor, and (c) a voltage insulation between the current conductorand the semiconductor die. The current conductor for the current to bemeasured is also referred to as primary conductor and the current to bemeasured also as primary current.

Embodiments of the present invention provide a printed circuit boardpackage (PCB package) comprising a printed circuit board that isarranged between a semiconductor die or semiconductor chip comprisingone or more core-less magnetic field sensors on one side of the printedcircuit board and the current conductor or primary conductor for thecurrent to be measured. The printed circuit board serves as mechanicalcarrier of the package (in particular during the production and, thusreplaces conventional mounting technologies using lead frames,semiconductor substrates or ceramic substrates as mechanical carriersduring the production) and at the same time insulates the sensor chip,also referred to as sensor semiconductor die, and the current conductorfrom each other. The sensor chip is hermetically sealed from theenvironment by the printed circuit board and an additional moldmaterial, wherein the sensor chip may be partially embedded in theprinted circuit board, e.g. in recesses in the printed circuit board. Inalternative embodiments sensor chip is hermetically sealed from theenvironment by the printed circuit board alone, e.g. is completelyembedded in the printed circuit board, e.g. in a multi-layer printedcircuit board.

Embodiments of the sensor package can be produced more cost efficientthan conventional sensors with ceramic carriers, semiconductor carriersor massive copper lead frames, both because their raw material is moreexpensive than printed circuit board material and because theprocessing, e.g. cutting, milling, drilling, punching, trimming, etc.,is more expensive than the processing of printed circuit board sensorpackages. In addition, there are inexpensive methods available toaccurately coat large panels of printed circuit boards with solder pasteor die attach or epoxy adhesives or insulating varnishes via ink-jetmachines.

Furthermore, the conducting layers can be made more accurately by wellestablished manufacturing techniques for printed circuit boardproduction. Particularly the alignment of the sensor chip and thecurrent conductor on opposite sides of the printed circuit board can beperformed more accurately using alignment structures or alignment markson the top of the printed circuit board layer, for example, on thesurface of the printed circuit board onto which the sensor chip is to bemounted. Similar alignment structures or marks are not known for leadframe, semiconductor or ceramic carrier based production technologies.

The printed circuit board can fulfill multiple purposes or tasks. It canserve as mechanical support of the sensor chip, as a voltage insulationbetween the sensor chip and the current conductor, and as a contactingmeans for the sensor chip, for example by providing the conductor traceson a surface of the printed circuit board facing towards the sensor chipor, for example in multi-layer printed circuit board designs, inside theprinted circuit board. In addition, the printed circuit board can holdthe current conductor and the sensor chip or sensor elements in a welldefined, stable distance, which helps to ensure a low lifetime drift ofthe current sensor. Core-less magnetic current sensors are verysensitive with regard to changes in their position or with regard to thedistance to the conductor whose current is to be measured. In contrastto magnetic current sensors comprising a core as macroscopic fluxconcentrator, core-less magnetic current sensors have no macroscopicflux concentrator which collects the flux around a conductor and guidesit onto the magnetic field sensor element. By hermetically sealing thesensor chip in the sensor package, or in other words by completelysurrounding the sensor chip by the printed circuit board material or theprinted circuit board material and the mold material, warpage due tomoisture or other environmental conditions of the sensor chip during thelifetime of the sensor package is avoided or at least reduced, and,thus, also a change of the vertical distance of the sensor chip and thecurrent conductor. Warpage of the sensor chip leads to a change of thevertical distance between the sensor chip and the magnetic field sensorwith regard to the current conductor and, thus, to a deterioration ordegradation of the measurement, signal, or in other words to a driftbetween the measured current intensity output by the sensor package andthe actual current over lifetime. By avoiding or reducing thepossibility of warpage, embodiments of the sensor package increase thereliability of the sensor package and the correctness of the measuredcurrent intensity.

In addition, conductor traces of the printed circuit board can bepatterned accurately with well established, cost efficient and reliableproduction techniques known for printed circuit board production, forexample etching. In particular, current conductors with fine slots, i.e.slots with very small dimensions, can be cost-efficiently and reliablyproduced.

Embodiments of the sensor package can comprise printed circuit boardsvoid of magnetic components which would distort the magnetic field (PCBscommonly use high purity copper for their traces) and reduce thestability and accuracy of the current sensor.

Embodiments of the sensor package can, furthermore, comprise thinconductive traces to serve as electrostatic shield and to contact thesensor chip or sensor semiconductor die, and there is no need for otherconductive parts in the printed circuit board, which avoids eddycurrents induced in the conductive parts by the magnetic field of thecurrent to be measured, which would reduce the bandwidth of the sensor.

Besides, printed circuit boards for high temperature operations orapplications are known. The problem of high temperatures is a commonproblem in current sensors due to dissipation caused by the largeprimary current in the current conductor, in particular in the case ofan over-current. The flame retardant properties of the FR4 family of theprinted circuit board materials can be used to overcome for example, thehigh temperature problem mentioned above.

Well known technologies for implementing contact regions on the printedcircuit board to connect the sense pins of the sensors or the sensorchip, i.e. all contacts except the ones for the primary current, can beused.

Printed circuit board packages are light weighted and mechanicallyrigid, yet not brittle.

In addition, the technology of printed circuit board production ismature also in the sense that it avoids peeling off of the conductinglayers and traces of the printed circuit board layer. This is a majorrisk for current sensors due to the combined action of thermo-mechanic,hygro-mechanic and electromagnetic forces at high currents, particularlyin the case of impulse loads (thermal cycling and mechanical cycling).The current flowing through the current conductor exerts a considerableforce on the current conductor or conducting layer, which isproportional to the square of the current amplitude. This force producedby the current tries to open up slots in the conducting layer producedto increase the intensity of the magnetic field by reducing thecross-section of the current conductor.

Finally, most printed circuit board materials have low relativedielectric constants of around 4.5. Low dielectric constants keep theunwanted capacitive crosstalk from the primary current layer or currentconductor to the sensor chip small.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention are described herein makingreference to the appended drawings.

FIG. 1A shows a schematic cross-section of an embodiment of a sensorpackage, wherein the sensor chip is hermetically sealed between theprinted circuit board and a mold body.

FIG. 1B shows top-views of structured current conductors comprising areduced cross section.

FIG. 1C shows a schematic cross-section of an embodiment of a sensorpackage, wherein the sensor chip is hermetically sealed by the printedcircuit board package.

FIG. 1D shows a schematic top-view of a sensor package according to FIG.1A and a current conductor for an I-shaped current flow.

FIG. 2 shows a cross-section of an embodiment of a sensor packagesimilar to the one of FIG. 1A, wherein the sensor chip is partiallyembedded in the printed circuit board and covered by a mold body.

FIG. 3 shows a schematic cross-section of an embodiment according toFIG. 1A with the sensor chip flip-chip mounted on the printed circuitboard package.

FIG. 4 shows a schematic cross-sectional view of an embodiment accordingto FIG. 1A with the sensor chip mounted face up on the printed circuitboard package.

FIG. 5 shows a schematic cross-sectional view of an embodiment accordingto FIG. 1A with a via through the printed circuit board to connect thesensor chip on the same side as the current conductor.

FIGS. 6A-6C show schematic cross-sectional views and a top-view ofalternative embodiments of the sensor package for connecting the sensorchip and the current conductor on the same side.

FIGS. 7A and 7B show schematic cross-sectional views of embodiments ofthe sensor package similar to FIG. 1A with enhanced protection againstlateral ingress of moisture into the printed circuit board package.

FIG. 8 shows a layout of an electrical connection of the sensor chip tothe sensor contact pads.

FIG. 9A shows a schematic cross-sectional view of an embodiment of thesensor package with a flip-chip mounted sensor chip and an additionalinsulation layer between the sensor chip and the printed circuit board.

FIG. 9B shows a schematic cross-sectional view of an embodiment of thesensor package with a face-up mounted sensor chip and an additionalinsulation layer between the sensor chip and the printed circuit board.

FIG. 10 shows a schematic cross-sectional view of an embodiment of thesensor package with an additional conducting layer arranged below theconductive layer.

FIG. 11 shows a schematic top-view of a further embodiment of thecurrent conductor with three slots.

FIG. 12 shows a schematic top-view of a prototype of an embodiment ofthe sensor package.

FIG. 13 shows a flow-chart of an embodiment of a method for producing anembodiment of the sensor package.

Equal or equivalent elements or elements with equal or equivalentfunctionality are denoted in the following description by equal orequivalent reference numerals.

DETAILED DESCRIPTION

Some aspects of the present disclosure are now set forth with regards tothe figures. It will be appreciated that all numerical references (e.g.,currents, voltages, lengths) are merely examples and do no limit thescope of the invention in any way. Also, all of these numerical valuesare only approximations, and actual values from vary from thoseexplicitly set forth herein.

FIG. 1A shows a schematic cross-sectional view of an embodiment of asensor package 100 comprising a printed circuit board 110 with a laminarcurrent conductor 120 arranged on a first main surface 110 a of theprinted circuit board, wherein a sensor chip 130 is adapted to measure acurrent flowing through the laminar current conductor 120. The sensorchip 130 comprises a magnetic field sensor 132 and optionally anevaluation unit (not shown). The sensor chip 130 is arranged on a secondmain surface 110 b of the printed circuit board opposite to the firstmain surface 110 a. The surfaces of the sensor chip 130 not covered bythe printed circuit board 110 (in FIG. 1A the side surfaces and the mainsurface facing away from the printed circuit board) are covered by amold body 140 comprising a mold material. Thus, the sensor chip 130 isarranged between the mold body 140 and the printed circuit board 110,wherein the mold body 140 and the printed circuit board 110 are arrangedsuch around the sensor chip that the sensor chip 130 is hermeticallysealed from the environment. In other words, the mold body 140 isarranged on the second main surface 110 b of the printed circuit boardand/or around the sensor chip 130 such that the sensor chip 130 isarranged between the mold body 140 and the printed circuit board and iscompletely surrounded by the mold body 140 and the printed circuit board110. The current conductor 120 comprises, for example, a first contactregion 122, a second contact region 124 and a magnetic field producingregion 126 arranged between the first contact region 122 and the secondcontact region 124 and electrically connecting both. The sensor chip 130and the magnetic field sensor 132 are associated to the currentconductor 120 or the magnetic field producing region 126 and are adaptedto measure a current flowing through the current conductor 120, forexample from the first contact region 122 via the magnetic fieldproducing region 126 to the second contact region 124, by measuring themagnetic field produced by the current. The current conductor 120 isalso referred to as primary conductor and the current flowing throughthe current conductor is also referred to as primary current. Note alsothat PCB 110 overlaps the sensor chip or die 130 along its entireperimeter by several tenths of a milli-meter in order to guarantee along enough creepage distance between conductor 120 and die 130 for thepurpose of voltage isolation.

Embodiments of the sensor package can be easily mounted on external andconventional circuit boards and connected to the conductors to bemeasured via the first and second contact region.

FIGS. 1A to 1D and the other figures show the respective axis 5′ of anx-y-z coordinate-system, wherein the x-axis and the y-axis define alateral plane or lateral dimensions parallel to the first main surface110 a of the printed circuit board, and wherein the z-axis defines avertical dimension vertical to the first main surface 110 a of theprinted circuit board.

FIG. 1B shows schematic top-views of three different embodiments of astructured current conductor 120. The embodiment of the currentconductor 120 shown in the top of FIG. 1B shows a patterned currentconductor 120 with a lateral notch 128 in the magnetic field producingregion 126 defining a laterally reduced cross-section 129 (note that 126is larger than 129, actually 129 is a part of 126). The reducedcross-section forms an area within the magnetic field producing region126 which has a reduced cross-section forcing the current flowing fromthe first contact region 122 to the second contact region 124 to flow“I”-shaped (see arrow A). The reduced cross-section and the bending ofthe current flow A caused by the notch 128 increases the current densityat the reduced cross-section (in particular at the inner side of thecurve arranged nearer to magnetic field sensor 132) and, thus, themagnetic field strength of the magnetic field produced by the current atthe reduced cross-section. This allows to increase the sensitivity ofthe current measurement. A possible lateral position of a magnetic fieldsensor element 132 of the sensor chip 130 for measuring the magneticfield of the current is shown by dotted lines.

The embodiment of the current conductor 120 shown in the middle of FIG.1B shows a “U”-shaped current flow (see arrow B). Similar to theaforementioned embodiment, the current conductor comprises a lateralnotch 128 in the magnetic field producing region and between the firstcontact region and the second contact region. However, in thisembodiment the first and second contact region 122 and 124 are arrangedonly on an opposite half of the current conductor, opposite to thereduced cross-section 129 in the magnetic field producing region 126.Thus, the current flowing from the first contact region 122 to thesecond contact region 124 is even more bent than in the aforementionedembodiment. In addition, the cross-section 129 of the embodiment shownin the middle of FIG. 1B is smaller than the cross-section 129 of theembodiment shown on the top of FIG. 1B, and, thus, even furtherincreases the magnetic field strength of the magnetic field produced bythe current. Again an exemplary position of a magnetic field sensor 132is shown.

The embodiment shown in the bottom of FIG. 1B shows a current conductorwith an “S”-shaped current flow (see arrow C). To achieve the S-shapedcurrent flow the magnetic field producing region 126 comprises twonotches arranged on opposite sides of the magnetic field producingregion 126 relative to the flow direction of the current and displacedor offset to each other in flow direction. In each of the notches 128,128′ a magnetic field sensor 132, 134 can be arranged to measure themagnetic field of the current. The use of two or more magnetic fieldsensors 132, 134 allows to use differential magnetic field measurementswhich compared to single magnetic field sensor measurements provideimproved sensitivity and signal robustness.

As can be seen from FIGS. 1A and 1B, the global direction of the currentflow of the patterned conducting layer 120 may be horizontal with regardto FIG. 1A or into the drawing plane of FIG. 1A or in any otherdirection parallel to the first main surface 110 a of the printedcircuit board and parallel to the first main surface 130 a of the sensorchip 130 facing towards the printed circuit board and the currentconductor 120. In other words, a current to be measured flows within thex-y plane parallel to the first main surface 130 a of the sensor chip130 from the first contact region to the second contact region. Thearrows A to C in FIG. 1B show the flow of the current when the currentor primary current is input at the first contact region 122 and isoutput at the second contact region 124.

Even further embodiments of the current conductor 120 may comprise otherpatterns and/or any number of and any form of slots or notches arrangedon any of the two opposite sides (with regard to the flow direction) ofthe magnetic field producing area 126 to bend the current and/or toprovide reduced cross-sections to increase the current density. Theimportant aspect is that at least one notch 128 is present in theprimary conductor and that at least one magnetic field sensor element132 is to be aligned with high precision (e.g. +/−150 μm or preferablyeven down to +/−10 μm in lateral direction and +/−5 μm or preferablydown to +/−50 μm in vertical direction) with respect to the notch.

Although such structured magnetic field producing regions 126 allow toimprove the sensitivity of the current measurement, simple embodimentsof the current conductor may also comprise a rectangular magnetic fieldproducing region 126 without any notches or other structures whichcombines the first contact region 122 and the second contact region 124.

The first and second contact regions 122, 124 may have the samethickness or vertical dimension (thickness of the conductor layer orheight hc) as the magnetic field producing region 126, or may have adifferent height. Embodiments of the sensor package can comprise, forexample thicker contact regions 122, 124 (larger vertical dimension) anda thinner magnetic field producing region 126 (smaller verticaldimension) in order to increase the current intensity in the magneticfield producing region 126 and, thus, the magnetic field onto themagnetic field sensors while keeping the internal resistance at aminimum.

Embodiments of the sensor chip may comprise only one single magneticfield sensor 132 as a single magnetic field sensor 132 is sufficient todetect a magnetic field of a current flowing through a conducting layer120. Other embodiments comprise at least two magnetic field sensors 132,134 to realize a differential measuring principle which allows tosuppress magnetic background disturbances.

As shown in FIG. 1A, the sensor chip 130 can be protected from theenvironment by over-molding it. According to an alternative embodimentthe sensor chip 130 can be protected from the environment by embeddingit into the printed circuit board 110′ as shown in FIG. 10. FIG. 10shows a cross-sectional view of the alternative embodiment, wherein thesensor chip is arranged in the printed circuit board 110 and ishermetically sealed by the printed circuit board. The embedding into theprinted circuit board 110 can, for example, be achieved by providing abase printed circuit board 110 as shown in FIG. 1A and arranging one orseveral other printed circuit boards on the base printed circuit board110 of FIG. 1A (multi-layer printed circuit board), wherein the printedcircuit board layer or printed circuit board abutting on the second mainsurface 110 b comprises a cavity on the surface facing towards the baseprinted circuit board 110 to incorporate the sensor chip 130. Thus, thesemiconductor die or sensor chip 130 is embedded between several layersof printed circuit board material as shown in FIG. 1C.

FIG. 1D shows a schematic top-view of an embodiment according to FIG. 1Awith a structured current conductor 120 according to the embodimentshown in the top of FIG. 1B. FIG. 1D shows the printed circuit board 110with the sensor chip 130 and the mold body 140 arranged on the secondmain surface (upper main surface according to the orientation of FIG.1A) and the current conductor 120 (broken lines) arranged on the firstmain surface (lower surface according to the orientation of FIG. 1A).The current conductor 120 comprises the first contact region 122, thesecond contact region 124 and the magnetic field producing region 126with a notch 129 on one side along the current flow direction defining areduced cross-section 129, as explained based on FIG. 1B. The sensorchip 130 comprises a single magnetic field sensor 132 arranged above thenotch 129 and laterally aligned to the notch 129, and the evaluationunit 136 electrically coupled to the magnetic field sensor 132 toevaluate the measurement signals of the magnetic field sensor(connecting lines between the magnetic field sensor 132 and theevaluation unit 136, or supply lines and signal lines for outputting themeasured signals by the evaluation unit 136 are not shown).

When a current flows through the current conductor 120, the currentproduces a radial magnetic field (radial to the current flow direction)which is measured by the magnetic field sensor. The magnetic fieldsensor can be for example, a Hall-sensor or magnetoresistive transducer,which provides, for example, a voltage signal proportional to themagnetic field strength. As the relation between the current, themagnetic field produced by the current and the voltage signal providedby the magnetic fields sensor based on the measured magnetic field isknown, the voltage signal provided by the magnetic field sensor 132 canbe mapped to a corresponding current value by the evaluation unit 136,in certain embodiments using a calibrations means, e.g. a calibrationtable or a calibration function, or in general a calibration informationor calibration data, to reduce a deviation between the measured currentintensity value according to the signal provided by the magnetic fieldsensor and the actual current intensity value of the current. Thecalibration data can, e.g., include values indicating how many mT(T=Tesla) magnetic field are produced by a current of 1 A.

To achieve an optimum measurement, the magnetic field sensor 132 isarranged near to the reduced cross-section, preferably vertically abovethe notch and near to the reduced cross-section (see also FIG. 1Ashowing in hash-dotted lines the optional reduced cross-section and thelateral alignment of the magnetic field sensor 132 with regard to thenotch or reduced cross-section). FIG. 1D shows the PCB overlapping boththe sensor chip and the primary conductor. In other embodiments the PCBoverlaps only the sensor chip, yet not the conductor: the PCB may besmall enough that both contact areas 122, 124 extend beyond it so thatthey may be contacted on their top or bottom surfaces (or even on both).

In certain embodiments, the thickness or vertical dimension hp of theprinted circuit board 110 right underneath the sensor chip 130, or inother words, the vertical dimension of the insulating area of theprinted circuit board 110 arranged between the sensor chip 130 and thecurrent conductor 120 for insulating both from each other, is smallerthan a vertical dimension hc (thickness or height) of the currentconductor or the magnetic field producing region 126 right underneaththe sensor chip 130. It has been found that the magnetic field of thecurrent conductor decays versus the vertical distance between thecurrent conductor and the magnetic field sensor or sensor chip and thespatial rate of decay scales with the thickness or vertical dimension ofthe conducting layer hc. Therefore, embodiments of the sensor bodycomprise printed circuit boards with a vertical dimension hp of theprinted circuit board (at least in the area arranged between the sensorchip and the current conductor insulating the two from each other) beingsmaller than a vertical dimension hc of the magnetic field producingregion 126 of the current conductor, so that a significant amount ofmagnetic field reaches up to the magnetic field sensors 132, 134.

Embodiments of the sensor package, however, may comprise not only theprinted circuit board as insulating layer between the sensor chip andthe current conductor (like in FIGS. 1A, 1C and 2) but may also comprisefurther insulating layers or other layers arranged between the sensorchip and the current conductor (see FIGS. 9A and 9B). In addition, thecurrent sensors may be flip-chip mounted (top-down, e.g. with themagnetic field sensor arranged near or at the main surface of the sensorchip facing toward the current conductor) or face-up (e.g. with themagnetic field sensor arranged near or at the main surface of the sensorchip facing away from the current conductor). Therefore, in general, forcertain embodiments the vertical dimension hc of the magnetic fieldproducing region vertical to the first main surface of the printedcircuit board is larger than a vertical distance hd vertical to thefirst main surface of the printed circuit board between one or allmagnetic field sensors associated to the current conductor and comprisedin the sensor chip and a surface of the current conductor, and inparticular of the magnetic field producing region, facing towards thesensor chip or magnetic field sensor. The vertical dimension hc of themagnetic field producing region can be more than 1.5 times larger ormore than 2 times larger than the vertical distance hd between themagnetic field sensor and the current conductor. In further embodimentsof the current sensor the magnetic field sensor is arranged such that avertical distance between the magnetic field sensor and the magneticfield producing region is larger than 50 μm and the vertical dimensionof the magnetic field producing region is larger than 100 μm. In evenfurther embodiments of the current sensor the magnetic field sensor isarranged such that a vertical distance between the magnetic field sensorand the magnetic field producing region is larger than 100 μm and thevertical dimension of the magnetic field producing region is larger than200 μm. In other embodiments, the vertical distance hd between themagnetic field producing region and the magnetic field sensor can be ina range between 50 μm to 200 μm and a vertical dimension of the magneticfield producing region in a range between 70 μm and 400 μm. Theaforementioned dimensions and relations apply independent of whether thesensor chip is only insulated from the current conductor by the printedcircuit board or by the printed circuit board and one or more otherinsulating layers, and independent of the vertical position of themagnetic field sensor within the sensor chip relative to the currentconductor (see FIGS. 9A and 9B).

In further embodiments, as shown in FIGS. 9A and 9B, the currentconductor can be electrically insulated from the sensor chip by aninsulating area of the printed circuit board arranged between the sensorchip and the current conductor and an additional insulating layerarranged between the sensor chip and the current conductor, wherein thevertical dimension he of the magnetic field producing region can belarger than a total vertical dimension hi+hp (see FIGS. 9A and 9B) ofthe insulating area of the printed circuit board and the additionalinsulating layer.

The vertical dimension hp of the printed circuit board in an area of theprinted circuit board arranged between the magnetic field producingregion and the sensor chip and the magnetic field producing region canbe larger than 50 μm and a vertical dimension of the current conductorlarger than 100 μm. In further embodiments, the vertical dimension hp ofthe printed circuit board in an area of the printed circuit boardarranged between the magnetic field producing region and the sensor chipcan be larger than 100 μm and the vertical dimension of the currentconductor larger than 200 μm. In other embodiments, the verticaldimension hp of the printed circuit board in an area of the printedcircuit board arranged between the magnetic field producing region andthe sensor chip can be in a range between 50 μm to 200 μm and a verticaldimension of the current conductor in a range between 70 μm and 400 μm.

A current conductor 120 or magnetic field producing region 126 with avertical dimension he that is larger than a vertical dimension hp of theprinted circuit board (see FIG. 1A, wherein the printed circuit boardhas everywhere the same vertical dimension hp) may lead—over the wholelifetime of the package—to warpage of the whole package and theassociated mechanical stress may lead to reliability problems. The riskof warpage can be reduced by keeping the thin part or region 110 i ofthe printed circuit board arranged between the sensor chip 130 and thecurrent conductor 120 as small as possible, or in other words, bykeeping the lateral dimensions of the thin intermediate or insulatingarea 110 i of the printed circuit board 110 as small as possible.

FIG. 2 shows a schematic cross-sectional view of an embodiment, whereinthe printed circuit board 110 comprises at its second main surface 110 ba recess to accommodate or contain the sensor chip 130. Thus, theprinted circuit board comprises only a small thin insulating area 110 i,insulating the sensor chip 130 from the current conductor 120, keepingthe distance between the sensor chip and the current conductor at aminimum (defined by the desired insulating voltage and depending on theprinted circuit board material) or as small as possible. Thus theposition the magnetic field sensor is as close as possible to thecurrent conductor and at the same time, the remaining areas or parts ofthe printed circuit board 110 (e.g. all parts or regions except 110 i)comprise a vertical dimension (thickness or height) sufficient toprevent or at least reduce the risk of warpage of the whole sensorpackage.

Warpage is even more effectively reduced in FIG. 1C. In this example, ifthe thickness of the PCB-material above the sensor chip is similar tothe thickness hp of the PCB-material below the sensor chip, then theforces of both parts are balanced and the package remains straight.

The magnetic field sensor 132 or the magnetic field sensors 132, 134 canbe arranged on the top or the bottom surface of the sensor chip 130. Ifthe magnetic field sensors are arranged on the bottom surface (see FIG.3) they are exposed to a larger magnetic field than on the top (see FIG.4), yet this typically involves a flip-chip mounting of the sensor chipor sensor die 130 onto the printed circuit board 110. In FIG. 3 thesensor chip 130 is mounted in a flip-chip style and contacted by thinconductive traces 112 on top of the printed circuit board. In FIG. 4 thesensor chip 130 is mounted with its front side containing the magneticfield sensors 132, 134 up and the contacts are made by bond wires 114.

FIG. 3 shows a schematic cross-sectional view of an embodiment of asensor package with the sensor chip or semiconductor die 130 arrangedface-down on the second main surface 110 b of the printed circuit board,for example via flip-chip mounting. The printed circuit board 110comprises besides the current conductor 120 on the first main surface,further conductor traces or conductive traces 112 on the second mainsurface 110 b to electrically connect the sensor chip 130. As can beseen from FIG. 3, the magnetic field sensors 132, 134 are arranged onthe main surface 130 a of the sensor chip 130 facing towards the printedcircuit board. In addition, the electrical contacts for connecting thesensor chip 130 or semiconductor die 130 to the conductive traces 112arranged on the second main surface 110 b of the printed circuit board(contacts not shown), are also arranged on the main surface 130 a of thesensor chip facing toward the printed circuit board. Thus, the magneticfield sensors are as close as possible to the current conductor and atthe same time, the electrical connection of the sensor chip, for examplefor power supply and for the output of the measured signals, can beefficiently and easily provided.

FIG. 4 shows a schematic cross-sectional view of a sensor package,wherein the magnetic field sensors 132, 134 and the electrical contactsfor connecting the sensor chip 130 to the conductive traces 112 arearranged on a main surface 130 b of the sensor chip facing away from theprinted circuit board. The electrical contacts (not shown) of the sensorchip 130 are connected via bond wires 114 to the conductive traces 112.Compared to the flip-chip mounting of FIG. 3, the face up mounting ofFIG. 4 facilitates increased reliability and reduced manufacturingcosts.

The printed circuit board 110 holds the sensor chip 130 in position (inparticular relative to the current conductor) and supports the sensorchip mechanically. Moreover, the printed circuit board establishes avoltage insulation between the sensor chip 130 and the current conductor120 by the insulating section or area 110 i of the printed circuitboard. In certain embodiments the printed circuit board overlaps thesensor chip 130 along its entire perimeter (see for example FIGS. 1A and1D), because even if the sensor chip is coated with some insulatingpolyimide, oxide or nitride-layer applied before dicing thesemiconductor wafer to produce the sensor chip or semiconductor die,this insulation often shows cracks and/or defects along the sewing edge.To protect at least these sawing edges of the sensor chip 130 againstthe conductor the printed circuit board overlaps the semiconductor chipin each of the lateral dimensions (x-y plane as shown in FIG. 1D).

The alignment of the sensor chip 130 and the current conductor 120 iscrucial because the magnetic field sensors 132, 134 have to bepositioned precisely with respect to the current conductor andeventually with respect to the lateral notches within the patternedcurrent conductor. The smaller, or the more pointed the ends of theslots in the current conductor according to FIG. 1B are the more themagnetic field will be concentrated near these ends. In other words, thesmaller the reduced cross-section 129 and the shorter the length of thereduced cross-section in flow direction is, the higher the magneticfield and the higher the concentration of a magnetic field near the endsof the notches. Therefore, to obtain an optimum measurement sensitivity,it is vital to locate the magnetic field sensors 132, 134 exactly atthese ends of the notches, as shown in FIG. 1B. However, with regard tothe production, the precise alignment is difficult as the opaque printedcircuit board is arranged between the current conductor and the sensorchip. Embodiments of the method for producing the sensor package,therefore, are adapted to include making visual marks on the top side110 b of the printed circuit board which help, for example an automateddie-bonder to find its place and to arrange the sensor chip and therespective magnetic field sensors precisely above these notch ends. Theuse of printed circuit boards as mechanical carriers for the sensorpackage production can benefit here from the experience of printedcircuit board manufacturers with regard to the manufacturing ofmulti-layer printed circuit boards with ultra-fine conductor traceswhere the alignment of various layers of the printed circuit board iscrucial for a correct interconnection of the printed circuit boardlayers, e.g. through conductive vias.

Printed circuit board based sensor packages are also beneficial withregard to the production of finely patterned magnetic field producingregions 126 of the current conductor 120, which generates the magneticfield. Certain embodiments of the sensor package comprise a structurecurrent conductor 120 with notches or slots 128 having, for example,radii of curvature of 50 μm to 200 μm. For example, in case the verticaldimension of the current conductor he is about 100 μm, the radius ofcurvature at the end of the notch is about 50 μm. In case the currentconductor 120 has a vertical dimension he of about 400 μm, the radius ofcurvature is about 100 μm to 200 μm. Again, for the production of suchstructured magnetic field producing regions 126 one can make use of theexisting know-how of printed circuit board manufacturers to manufacturesuch conductive layers 120, 126 with sufficient accuracy, for examplevia mechanical or chemical processes like milling or etching.

Embodiments of the sensor package may further be adapted such that allcontacts, the high current contacts for the current conductor and thesmall sense contacts and power supply contacts for the sensor chip, areavailable on the same surface or side of the package as shown in FIG. 5.FIG. 5 shows a schematic cross-sectional view of a sensor packagecomprising a printed circuit board 110 with a protruding part 510protruding in vertical direction (z-axis). The protruding portion 510protrudes in direction of the current conductor 120, or in other words,protrudes away from the sensor chip 130 and has, for example, the samevertical dimension as the current conductor 120. The conductive traces112 connecting the sensor chip 130 are connected through conductive vias512 arranged vertically in the printed circuit board 110 and theprotruding portion 510 to the sense contacts 514 arranged on the firstmain surface 510 a. The surface of the sense or sensor contacts 514 arearranged flush with the surface of the current conductor facing awayfrom the printed circuit board.

The sensor chip 130 in FIG. 5 is arranged face-down, or in other wordsvia a flip-chip mounting, on the second main surface 110 b of theprinted circuit board and is connected via contacts (not shown) arrangedon the first main surface 130 a of the sensor chip to conductive traces112.

An alternative embodiment is described based on FIGS. 6A and 6B, whereinFIG. 6A shows a schematic cross-section view of the embodiment andwherein FIG. 6B shows a schematic top-view of the embodiment. FIG. 6Bshows a top-view of the embodiment according to FIG. 6A with theadditional printed circuit board layer 610 removed to give sight to thesensor chip. In this alternative embodiment the massive contacts for theprimary current to be measured can be brought up to the top surface(orientation according to FIG. 6A) of the sensor package and the sensorpackage can be used, for example, upside down. The sensor chip in FIG.6A is flip-chip mounted, or in other words, is mounted face-down, on theprinted circuit board 110. Two magnetic field sensors 132, 134 and theelectrical contacts for connecting the sensor chip 130 are arranged onthe first main surface 130 a of the sensor chip facing towards theprinted circuit board 110. The electrical contacts of the sensor chipare connected to conductive traces 112 arranged on the second mainsurface of the printed circuit board. A further or upper printed circuitboard layer 610, for example similar to the embodiment described basedon FIG. 1C, is arranged on the printed circuit board 110 and the sensorchip 130 and completely seals and surrounds the sensor chip 130. Withinthe additional printed circuit board layer 610, a vertical electricallyconducting via 614 is arranged and connects the conductive traces 112 tothe sensor contacts 616 arranged on the main surface of the additionalprinted circuit board layer 610 facing away from the printed circuitboard 110.

FIG. 6B shows the sensor chip 113 with three magnetic field sensors 132,134, 136, for example three Hall plates arranged lateral to each other,wherein the sensor chip 130 is connected via three fine conductivetraces 112 a, 112 b and 112 c, arranged on the second main surface ofthe printed circuit board 110 to respective three vias 614 a, 614 b and614 c, which are again connected to three sensor contacts 616 a, 616 band 616 c. FIG. 6B additionally shows the massive contacts for theprimary current contact 614 connected via the vertical via 622 to thefirst contact region 122 and a second primary current contact 634connected via a second massive conductive via 624 arranged in anadditional printed circuit board layer 610 and eventually also in theprinted circuit board 110, to the second contact region 124 of thecurrent conductor. Further embodiments may comprise instead of a singlemassive via a large number of smaller vias electrically connected inparallel and geometrically arranged in a matrix form.

The dotted line in FIG. 6B shows the edge or circumference of theconductive layer or current conductor 120. The current conductor 120comprises three slots 128 a, 128 b and 128 c arranged on opposite sidesof the current conductor with regard to the current flow direction todefine a “W” current flow. A plain view of one of the printed circuitboard layers 110, 610 or of both printed circuit board layers may have ashape of an “H” (see FIG. 6B) in order to give a passage for the currentto be measured.

FIG. 6C shows an alternative embodiment to FIG. 6A, wherein the contacts632, 634 for the current to be measured can be part of the additionalprinted circuit board layer 610 and are coupled to the lower conductinglayer 120 by numerous vias 642 and 644 to pass the high current through.

Environmental conditions may cause problems with regard to the sensorchip and its correct vertical and lateral positioning with regard to thecurrent conductor 120, but may also affect other parts of the sensorchip. For example, lateral ingress of moisture into the printed circuitboard 110 may cause major problems because the moisture may destroy thelaminar structure of the printed circuit board or it may lead todwelling of the printed circuit board thickness (e.g. its verticaldimension hp), which would cause a drift in the reading of the current,similar to the bending of the sensor chip alone. This is all the moresevere as the sensor package is much smaller than ordinary printedcircuit boards which hold and connect numerous devices and have e.g. 100times longer migration paths for moisture compared to embodiments of thesensor package. Therefore, embodiments of the present invention comprisesome isolation barrier against the moisture soaking of the printedcircuit board. Such barriers can be, for example, a ring of wires, bycoating the flush surfaces of the printed circuit board 110 withmoisture-resistant varnish or grease 710 as shown in FIG. 7A, or byover-molding the entire printed circuit board as shown in FIG. 7B. FIG.7B shows the mold body 140′ not only hermetically sealing the sensor130, but also the printed circuit board 110 from the environment. It isalso possible to wrap up the printed circuit board with a moistureresistant foil or to cover its top surface with a foil, which overlapsthe side walls, when it is wrapped around them. The foil can be fixed tothe printed circuit board by adhesives.

It is possible to integrate further electronic components intoembodiments of the printed circuit board package. In particular, it isfavorable to connect a ceramic capacitor between supply pins of thesensor circuit 130, especially if the sensor circuit 130 is an activeintegrated circuit with a large digital part on it, which draws largecurrents at each clocking event. Since the rise time of the clocks iswell below 10 ns, the tank capacitor needed to stabilize the supplyneeds to be as close as possible to the integrated circuit 130,otherwise it would be ineffective due to large series inductance causedby the long leads. On the other hand, most capacitors use at leastpartial magnetic materials. Thus, these capacitors would interfere withthe magnetic field of the primary current to be measured and cause ameasurement error. Therefore, moving the responsibility of selectingthis sensitive device (the tank capacitor) and of trimming the entiresensor chip 130 after the package has been fully assembled to thesemiconductor manufacturer allows to account for residual magnetism ofthe capacitor, to perform a calibration sequence of the whole currentsensor and to provide a high sensitivity and accuracy current sensor bythe manufacturer. Users of the sensor package do not have to deal withsuch aspects and the design-in of such sensor packages is facilitated.

Further embodiments of the sensor package comprise especially thin wires112 to contact the sensor chip 130. Thus, in case of an accidentalshort-circuit between the primary current circuit and the semiconductorsensor, for example, due to malfunctioning of the insulating printedcircuit board-layer 110 between the two, the thin wires 112 act as fusesand blow before transferring a lethal amount of charge to the pins ofthe sensor chip 130. Again, the use of a printed circuit board as acarrier for the sensor package is beneficial as it allows to producefine long traces 112 on the second main surface of the printed circuitboard to contact the sensor chip 130. Moreover, it is possible toconnect a passive device such as a protection resistor or diode or adiscrete fuse device into the supply and signal lines of thesemiconductor die 130. An embodiment of the sensor package comprisingsome of the aforementioned features is shown in FIG. 8. FIG. 8 shows alayout of sensor chip 130 and its connection to connecting pads of thesensor package. FIG. 8 shows the sensor package comprising threemagnetic field sensors 132, 134 and 136 and three contact pads 832, 834and 836, wherein the contact pad 836 forms the out-pad (OUT) of thesensor package for outputting the measured current value, contact pad834 (GND) forms the ground pad of the sensor package and contact pad 832forms the voltage supply pad (VDD) for supplying power to the sensorchip 130. The out-pad 836 is connected via a fast fuse 824C to a contactpad 816 c (OUT) of the sensor package. Ground pad 834 is connected via aconductive trace 112 b and a second fast fuse 824 b arranged in seriesto a connecting line 112 b to a ground pad 816 b (GND) of the sensorpackage. Power supply pad 832 is connected via a third conductive trace112 a and a third fast fuse 824 a to a power supply pad 816 a (VDD) ofthe sensor package. The fast fuses 824 a,b,c blow in case ofover-current, i.e. in case the current exceeds a certain thresholdcurrent. In particular embodiments of the sensor package all pins 832,834 and 836 are protected by fuses or thin conductor traces, which actlike fuses, to provide a save protection of the sense pins VDD, GND andOUT or 832, 834 and 836. In addition, a first voltage stabilizingcapacitor 822 a is connected between the conductive traces 112 a and 112b and a second voltage stabilizing capacitor 822 b is connected betweenthe conductive traces 812 c and 812 b. In other words, the sensor chip130 is connected via ample conductive traces 112 a, 112 b and 112 c to acapacitor and a series fuse in each line, whereby the distance dc of thecapacitor and the fuses to the sensor chip 130 is large enough toguarantee no magnetic interference onto the sensor operation. Theconductive traces or bond wires are thick enough to have sufficientlysmall resistance and inductance. Other embodiments of the sensor packagemay comprise, besides the sensor chip, one or several discrete circuitelements, e.g. discrete circuit elements not integrated into the sensorchip, coupled between a pin or a contact of the sensor chips, forexample, 832, 834 and 836, and an external contact or contact pad of thesensor package, for example, 816 a, 816 b and 816 c. Typically suchdiscrete circuit elements comprise lead frames and/or contacts withnickel (Ni) plating or other materials which are magnetic. To reducedisturbances of the measurement of the magnetic field of the current bymagnetic fields caused by these discrete circuit elements or by magneticmaterials used in their construction, one or all of these discretecircuit elements of embodiments of the sensor package comprise onlymaterial with a relative permeability of less than 1.1 or in case thediscrete circuit elements comprise material with a relative permeabilityof 1.1 or more than 1.1 the discrete circuit elements are arrangedspaced apart from the magnetic field sensor by at least 1.5 mm. In evenfurther embodiments, the sensor package 100 does not comprise anydiscrete circuit elements with a relative permeability of more than 1.1that is arranged in a distance smaller than 1.5 mm to any magnetic fieldsensor element of the sensor chip. The discrete circuit elementsdescribed above comprise, for example, capacitors, fuses and/orelectrical conductors including the conductive traces 112 laminated onthe printed circuit board.

Common printed circuit board materials can establish a voltageinsulation of 4 kV at thicknesses or vertical dimensions (z-axis) of 150μm. If, for example, even higher voltage insulation of up to 12 kV isneeded, additional insulation layers like polyimide layers, for examplecomprising or made of Kapton, can be arranged between the printedcircuit board 110 and the sensor chip 113. FIG. 9A shows an embodimentof a sensor package with a printed circuit board 110 comprising a cavityon a second surface 110 b, in which the sensor chip 130 is arranged and,wherein between the sensor chip and the printed circuit board 110 anadditional insulation layer 910 is arranged to increase the voltageinsulation or dielectric strength. In contrast to the embodimentaccording to FIG. 2, the cavity has larger lateral and verticaldimensions than the sensor chip 130 and also a vertical dimension largerthan a combined vertical dimension of the sensor chip 130 and theadditional insulating layer 910, so that the mold material 140 is usedto completely fill the cavity and to thus seal the sensor chip 130 fromthe environment. As can be seen from FIG. 9A, the main surface of themold body 140 facing away from the current conductor has the same heightlevel as the printed circuit board 110. For such embodiments thecontacts to the sensor chip 130 can be made via thin traces of copper onthe top surface of the additional insulating layer, for example a Kaptontape, if the sensor chip is mounted upside-down or via simple bond wiresif the sensor chip 130 is mounted face-up.

Whereas FIG. 9A shows a schematic cross-sectional view of an embodimentof the sensor package with a flip-chip mounted sensor chip and anadditional insulation layer between the sensor chip and the printedcircuit board, FIG. 9B shows a schematic cross-sectional view of analternative embodiment of the sensor package with a face-up mountedsensor chip and an additional insulation layer between the sensor chipand the printed circuit board. The term he refers to the verticaldimension of the magnetic field producing region vertical to the firstmain surface 110 a of the printed circuit board 110, hp refers to thevertical dimension of the region 110 i of the printed circuit board 110arranged between the sensor chip 130 and the magnetic field producingregion 126 of the current conductor 120 (see also FIG. 10 or 2), hirefers to the vertical dimension of the insulating layer or the regionof the insulating layer arranged between the sensor chip 130 and themagnetic field producing region 126, and hd refers to the verticaldistance between one or all magnetic field sensors associated to thecurrent conductor and comprised in the sensor chip and the surface 110 aof the current conductor facing towards the sensor chip or magneticfield sensor 132. As can be seen from FIG. 9A (top down mounting of thesensor chip), the vertical distance hd roughly corresponds (in case themagnetic field sensor is arranged near or at the surface 130 a of thesensor chip facing towards the current conductor) to the verticaldimension of the printed circuit board hp (in case no other layers arearranged between the sensor chip and the current conductor, or to thetotal of the individual vertical dimensions, e.g. hi+hp, in case one ormore insulating or dielectric layers are between the sensor chip and thecurrent conductor. In case of face-up mounted sensor packages or sensorpackages, wherein the magnetic field sensor is arranged near or at thesurface 130 b of the sensor chip facing away from the current conductor(see FIG. 9B), the distance of the magnetic field sensor to the surface130 a of the sensor chip is also included in the vertical distance hd.

It is possible to add another conductor at the bottom of the package,for example, by arranging the current conductor 120 onto this additionalconductor. FIG. 10 shows a schematic cross-sectional view of anembodiment of the sensor package with an additional current conductor1020 arranged on the main surface 120 a facing away from the sensor chip130. The vertical dimension of this additional current conductor 1020 islarger than the vertical dimension of the current conductor 120. Thus, aseries resistance of the additional current conductor 1020 is smallerthan a series resistance of the current conductor 120. This keeps thedissipation low and allows to reduce the dissipation considerably whilekeeping the magnetic field produced by the magnetic field producingregion 126 still high. In certain embodiments the vertical dimension ofthe additional conductor layer is 2 times larger than the verticaldimension he of the current conductor, or 5 times larger. The layer 1020can be a coarsely patterned thick conducting layer 120 and the layer 120a finely patterned thin conducing layer.

FIG. 11 shows a further embodiment of the current conductor 120, whereinthe magnetic field producing region 126 comprises two notches 1028 and1028′ arranged opposite to each other with regard to the current flowdirection such that the two notches 1028 and 1028′ define a centralreduced cross-section, wherein additionally three slits 128, 128′ and128″ are arranged on opposite sides of the reduced cross-section to bendthe current flow according to a “W”-shape (see arrow D). The reducedcross-section and the additional bending of the current by the slotsincreases the magnetic field at the slots and provides basis for a highsensitivity current measurement by magnetic field sensors arranged abovethe ends of the slots 128, 128′, 128″. The two slots 128 and 128′ reachfrom the top downwards (with regard to the orientation of FIG. 11) andthe central slot 128′ reaches from the bottom up (with regard to theorientation of FIG. 11).

FIG. 12 shows a schematic top-view of a sensor package with a currentconductor similar to the one shown in FIG. 11 (with three slots, two onone side and the central slot on the opposite side with regard to theflow direction). FIG. 12 shows the three slots 128, 128′ and 128″, thesensor chip 130 with contact pads 1232, 1234 and 1236, wherein thecontact pads 1232 of the sensor chip 130 are connected via bond wires114 a to conductive traces 112 a and the contact pads 1234 and 1236 ofthe sensor chip 130 are connected by bond wires 114 b to conductivetraces 112 b. For demonstration purposes only one transparent varnishwas used as insulation layer between the current conductor and thesensor chip 130.

FIG. 13 shows a flow chart of a method for producing a sensor package.The method for producing a sensor package comprises, providing 1310 aprinted circuit board with a laminar current conductor arranged on afirst main surface of the printed circuit board, and providing 1320 asensor chip adapted to measure a current flowing through the laminarcurrent conductor, wherein the sensor chip comprises a magnetic fieldsensor. According to a first embodiment, the method further comprisesarranging 1330 the sensor chip on a second main surface of the printedcircuit board opposite to the first main surface such that the sensorchip is electrically insulated by the printed circuit board from thecurrent conductor, and hermetically sealing 1340 the sensor chip betweena mold material and a printed circuit board.

According to a second alternative embodiment of the method, the methodcomprises arranging 1350 a sensor chip in the printed circuit board suchthat the sensor chip is electrically insulated by the printed circuitboard from the current conductor and such that the sensor chip ishermetically sealed.

Further embodiments of the method comprise arranging the sensor chip onthe second main surface of the printed circuit board using alignmentstructures or alignment marks arranged on the second main surface.

Even further embodiments comprise producing the sensor chip in a printedcircuit board panel comprising a plurality of sensor chips, wherein oneor all of the steps of producing and testing are performed with thesensor chip arranged in the printed circuit board panel. In addition,the sensor package can be isolated from the printed circuit board panelafter an end-of-line test, wherein the sensor chip is testedindividually (in parallel or in series) from other sensor chips of theprinted circuit board panel.

Further embodiments of the method comprise calibrating the sensorpackage, e.g. before isolating the sensor chip from the circuit boardpanel. The calibration comprises applying a current of a known intensityto the current conductor, measuring the current or obtaining the signalof the magnetic field sensor or the sensor chip associated to thecurrent, comparing the known intensity of the current with the measuredintensity of the current and determining a deviation between the knownintensity of the current and the measured intensity of the current andapplying a correction of the measured value to reduce the deviation sothat after the calibration the evaluation unit outputs the correctcurrent intensity value. The correction can be performed by theevaluation unit, e.g. by mapping the signal provided by the magneticfield sensor and/or mapping a value obtained based on this value to anoutput value provided in a mapping table (calibration table) orcalculated based on a mapping function (calibration function).

In certain embodiments the calibration is performed after the completesensor chip has been packaged, e.g. after the sensor chip and any otheroptional discrete circuit element has been sealed by the printed circuitboard and/or the sealing material, and only the external contacts orpads, e.g. 816 a, 816 b, 816 c, of the sensor package remain forelectrically connecting the sensor chip. Thus, any production variation,e.g. with regard to the electrical characteristics of the sensor chip,the one or more magnetic field sensors comprised in the sensor chip andthe individual discrete circuit elements and/or any productionvariation, e.g. with regard to assembling and structuring variationslike the position, structure and dimensions of the current conductor andthe relative position of the magnetic field sensors with regard to thecurrent conductor and the optional notches or slits, can be correctedusing calibration information stored in the sensor chip or sensorpackage to obtain a reliable and high accuracy current sensor package atlow cost.

The printed circuit board packages have a lower thermal mass than leadframe packages and, thus, smaller thermal settling times and shortercalibration times, in particular, when calibrating the sensor package atdifferent temperatures. Thus, the production of PCB current sensorpackages, as described above, have lower production costs compared toconventional lead frame based current sensor packages.

Further embodiments of the sensor package can comprise a housing orpackage for an integrated circuit 130 with one or several magnetic fieldsensor elements 132, which measures the electric current flowing throughthe current conductor 120 by measuring the magnetic field coupled to thecurrent. These packages 100 comprise a current conductor 120, a printedcircuit board or printed circuit board intermediate layer 110 and anintegrated semiconductor chip 130 hermetically sealed by the printedcircuit board or by the printed circuit board and molding material.

Further developments of such embodiments may comprise a currentconductor 120 with a laminar shape, i.e. the lateral dimensions of thecurrent conductor in both extension directions (x and y axis) areconsiderably larger than the vertical dimension (z-axis) of the currentconductor.

In further developments of such embodiments the current conductor maycomprise two contact regions 122, 124 and a magnetic field producingmiddle area 126 arranged in-between the two contact regions, whereineach of the contact regions and also the magnetic field producing region126 comprises a larger area (extension with regard to the lateraldimensions) than the semiconductor chip 130, and/or wherein the magneticfield producing region 126 has a vertical dimension (z-axis) larger thanthe printed circuit board intermediate layer 110.

In further developments of such embodiments the printed circuit boardintermediate layer 110 can be arranged such that a dielectric strengthof at least 1000 V is accomplished and/or the printed circuit boardintermediate layer 110 can be adapted to have no magnetic components andno conducting areas for large circular eddy currents, for example, eddycurrents with a diameter of more than 1 mm.

In further developments of such embodiments the printed circuit boardforms a means to mechanically support and electrically connectelectronic components via conductive traces, for example, etched fromcopper sheets laminated onto a non-conductive board comprising aninsulating or dielectric composite material. The composite materialsused for circuit board production are, for example, made up of two ormore different materials which remain separate and distinct on amicroscopic level within the finished structure. Typically twocategories of materials of producing composite material aredistinguished, matrix material and reinforcement material, wherein theenforcement material reinforces the matrix material to provide the rigidcomposite material or composite structure. Matrix materials are oftenpolymeric materials, also referred to as resin solutions, whereas forreinforcement materials often fibers, but also woven sheets of paper areused. Well-known composite materials used for printed circuit boardsare, for example, FR-2 (phenolic cotton paper) FR-3 (cotton paper andepoxy), FR-4 (woven glass and epoxy), FR-5 (woven glass and epoxy), G-10(woven glass and epoxy), CEM-1 (cotton paper and epoxy), CEM-2 (cottonpaper and epoxy), CEM-3 (woven glass and epoxy), CEM-4 (woven glass andepoxy), CEM-5 (woven glass and polyester). In particular the FRcomposites are commonly used due to their flame-retardness (FR-flameretardant).

Typically, a layer of copper is coated or laminated over the entiresubstrate, on one side or on both sides. To produce the wantedconductive traces or conductors, e.g. the conductive carrier 120 or theconductive traces 112, the unwanted core parts are removed. Besidesthese subtractive methods also additive processes are known forproducing the conductive traces. Thin conductive traces can, forexample, be galvanically treated to produce conductors with largervertical dimensions or thicknesses. Several printed circuit boards canbe stacked to form multi-layer printed circuit boards. The conductors ofthe different printed circuit boards within a multi-layer printedcircuit board can be connected to each other through conductive vias.

Laminar current conductors allow to bring the current close enough tothe sensor on one hand and at the same time to keep the internalresistance of the conductor minimal, to optimize the thermal couplingbetween the current conductor and the sensor chip and to provide astrong mechanical connection through a large bonding surface whichremains stable within a micrometer range over the whole lifetime of thesensor package.

The contact regions 122 and 124 have a major influence on the internalresistance of the current conductor. In certain embodiments the contactregions 122 and 124 are arranged such that the current is bent only to aminimum extent when passing from the first current conductor to themagnetic field producing region (current input) and when passing fromthe magnetic field producing region to a second contact region. (currentoutput). Additionally, the contact regions typically do not change themagnetic field at the position of the magnetic field sensors even incase the exact geometry of the contact positions varies, for examplebecause the contacts are not soldered all over or the current providingconductor is not soldered at the center of the first or second contactregion.

In further embodiments, the magnetic field producing region comprises atleast one slot or one diminution, or in other words at least one featureat which the current lines are bent strongly and/or the current densityis increased considerably.

The circuit for a semiconductor chip 130 for measuring the magneticfield of a conductor can require, e.g. about 7 mm². Embodiments of thesensor package with current sensors for currents in a range between 20 Aand 500 A, thus, can comprise internal resistances within a range of 20μΩ to 200 μΩ. The sensor chip may, for example, have lateral dimensionsof 2.6 mm×2.6 mm or 2 mm (dimension in x-direction)×3.5 mm (dimension iny-direction or flow direction). The sensor packages comprising suchsensor chips may comprise magnetic field producing regions with alateral dimension of 3 mm in flow direction (x-direction) and at least 4mm in a lateral dimension perpendicular to the flow direction of thecurrent (y-direction). In case the magnetic field-producing region has avertical dimension (thickness) of 0.1 mm, the resistance of the magneticfield-producing area is about 20 μΩ (for copper). Due to the reducedcross sections, the resistance is increased to roughly 30 μΩ to 50 μΩdepending on the form and number of the notches and slits. In addition,the contact regions have an additional own resistance and there is afurther resistance portion, because the current flow from the largercontact region to the smaller magnetic field-producing region iscompressed. Therefore, current conductors with a vertical thickness of0.1 mm to 0.4 mm have resistance values of about 20 μΩ to 2 mΩ or 3 mΩ.

Further embodiments of the magnetic field-producing region have, forexample, lateral dimensions of 5 mm×5 mm. The contact regions for 20A-current sensors are smaller, for 200 A-current sensors, each of thecontact regions again covers roughly an area of 25 mm², however,typically not quadratic, but with a shorter lateral dimension in theflow direction and a longer lateral dimension perpendicular to thecurrent flow direction.

A vertical dimension of the magnetic field producing region 126 defineshow strong the magnetic field drops or decreases with an increase of thevertical distance from the current conductor surface. Therefore, thevertical dimension of the current conductor is, e.g., chosen to belarger than the vertical dimension of the insulating layer, for examplethe printed circuit board intermediate layer 110 or 110 i, or anycombination of or a stack of insulating layers so that sufficientmagnetic field couples over the insulating layer to the magnetic fieldsensor.

Therefore, in one implementation the printed circuit board 110 has,e.g., a minimum vertical dimension of 100 μm, no conductive vias betweenthe opposite main surfaces in the region below and right next to thechip and overlaps the borders of the sensor chip 130 by at least 0.2 mm.

Copper laminations used in conventional circuit boards are often platedusing nickel. However, in the neighborhood of the magnetic fieldsensors, for example within the distance of less than 1.5 mm, materialswith a coercive force of more than 1 A/m are often avoided so as to notdisturb the measurement of the magnetic field.

Further embodiments of the sensor package comprise a first and a secondcontact region 122, 124 which are not covered by the printed circuitboard intermediate layer 110. In other words the contact regions 122 and124 are directly accessible from both sides. This is prevalent in someinstances, for example, if the sensor package is bolted to massive busbars or welded using an ultrasonic nozzle to external conductors.Further, external conductors can be welded to the contact regions usingan ultrasonic nozzle, for example.

Further embodiments of the sensor package comprise a magnetic fieldproducing region 126 with at least one structural element that effects astrong inhomogenity of the current density, for example through anincrease by 150% or more (with 100% referring to the average currentdensity at the contact area), or a strong bending of the current lines,for example by more than +/−40° compared to a main current direction ora virtual direct connection between the first contact region and thesecond contact region, and wherein the magnetic field sensor element isarranged right above this cavity or slot with a tolerance of +/−1.2 mm.

According to a further embodiment, a sensor chip 130 comprises a memorymeans for storage of calibration information, for example anEEPROM-memory (EEPROM—electrically erasable programmable memory) or somekind of analog memory like laser-trimming of resistors and the sensorpackage is produced in a printed circuit board panel so that a costefficient calibration in mass production through a test-in-strip-handler(perhaps even at several temperatures) is possible. One aspect of thisembodiment is that each device or sensor package has its own, individualcalibration information, which accounts for position tolerances of thecurrent conductor with respect to the magnetic field sensor elements.

According to another embodiment, the sensor package 130 is produced in aprinted circuit board panel such that the PCB-panel can be isolatedafter an end-off-line-test, by punching or snapping the individualpackages out of the PCB-panel. It should be noted that conventionalsensor-packages are produced and tested in a copper panel. However, inthese conventional sensor-packages the copper is too thick for isolatingthe individual packages easily, for example by punching. In addition,the copper forms an electric coupling of the individual devices in thecopper-panel so that the individual devices cannot be powered or testedindividually and independently from each other. In contrast thereto,some aspects of this disclosure use a printed circuit board as carrierfor the production and producing the sensor package within a printedcircuit board panel, such that the individual sensor packages cannotonly be easily isolated but also individually tested within a printedcircuit board panel.

According to another embodiment, the printed circuit board intermediatelayer 110 is sealed at its periphery so that a dwelling of the laminarstructure due to humidity or a delamination due to life cycle stress,for example cycle stress, can be avoided or limited. A sealing of theprinted circuit board can be performed by finish, coating via sprayingor with a foil, evaporation or molding.

According to another embodiment, the printed circuit board 110 compriseson a main surface on which the sensor chip is arranged, a thin conductorlayer, for example a copper lamination, which either serves as anelectrostatic shield or as contact for the sensor chip or as means forbonding the sensor chip via soldering, in particular via diffusionsoldering.

According to another embodiment, the printed circuit board 110 compriseson a first main surface in which the current conductor 120 is arranged,a thin conductor layer, for example a copper lamination, which iselectrically connected to the current conductor, for example bysoldering, e.g. diffusion soldering, or bonding within conductiveadhesive. The thin conductor layer or conductor layer can provide aparticularly stable, also temperature stable, mechanical connection orcan be used to self-center the printed circuit board layer relative tothe current conductor through the surface tension of the solder or theadhesive.

According to another embodiment the printed circuit board 110 comprisesa thin conductive layer on the second main surface on which the sensorchip is mounted, for example a copper lamination, serving as contactmeans for the sensor chip, wherein the integrated circuit or sensor chipis mounted face-down on the printed circuit board such that bond pathsof the sensor chip are contacted to the copper lamination via solderballs, solder bumps or conductive adhesive.

According to another embodiment a printed circuit board intermediatelayer 130 comprises a thin conductive layer, for example a copperlamination, on the second main surface of the chip upon which the sensorchip is mounted, wherein the sensor chip is mounted face-up on theprinted circuit board and the electrical connection between the bondpaths and the conductive traces on the printed circuit board is realizedvia bond wires. According to another embodiment, the printed circuitboard intermediate layer comprises means for centering upon the currentconductor, for example mating boreholes or grooves.

According to another embodiment all contact regions of the printedcircuit board do not comprise a lamination with permeable materials witha relative permeability of more than 1.1 or are arranged in a distanceof at minimum 1.5 mm to the magnetic field sensor elements.

According to another embodiment the contact regions of the currentconductor and the contacts of the sensor chip are arranged in one planesuch that the sensor package is suitable for a surface mount assembly.

According to another embodiment, the magnetic field producing region ofthe current conductor has a vertical dimension at its thinnest sectionof at least 0.2 mm.

According to a further embodiment the dielectric strength of the printedcircuit board intermediate layer 130 is strengthened by a laminatedpolyimide layer, for example a Kapton foil, for example with a verticaldimension smaller than 0.2 mm, and in particular within a range of 50 μmto 125 μm.

According to another embodiment the sensor chip is completely surroundedby printed circuit board material. In other words, the sensor chip 130is laminated into the printed circuit material such that the printedcircuit board is not only arranged between the sensor chip and thecurrent conductor but the sensor chip is also covered by the printedcircuit board on the remaining top main surface facing away from thecurrent conductor.

To reduce or avoid eddy currents, particular embodiments of the sensorpackage as described based on FIGS. 1A to 12 only comprise the printedcircuit board or other dielectric layers or material between the sensorchip 130 and the magnetic field-producing area 126 and do not compriseany electrically-conductive layers, in particular, no massive conductivelayers with particular dimensions of more than 100 μm (unlike typicallead frame packages). Therefore, embodiments of the sensor package withface-up mounted sensor chips, as shown in FIG. 4, do not comprise anyelectrically conductive layers or structures between the sensor chip 130and the current conductor 120 and, in particular, not between any of themagnetic field sensors 132, 134 (associated to the current conductor andthe magnetic field-producing region 126) and the magneticfield-producing region 126. Therefore, certain embodiments of the sensorpackage comprising a flip-chip mounted or top-down mounted sensor chip130, as shown in FIG. 3, only comprise thin lateral conductive traces toconnect the sensor chip, for example, to connect the power supply pins,control pins and output pins of the sensor chip 130 to other discreteelectric components integrated in the sensor package or to the contactpads for the external connection of the sensor package, between thesensor chip 130 and the current conductor 120 and do not comprise anyfurther conductive structures or layers between the sensor chip and thecurrent conductor. In addition, these thin lateral conductive traces arenot arranged between the magnetic field sensors and the magnetic fieldproducing region.

Further embodiments of the sensor package may comprise an insulationarranged on a surface of the current conductor or additional currentconductor covering a part of the surface or the entire surface. Thisinsulation can be, e.g., a further printed circuit board layer or asolder stopping layer.

Depending on certain implementation requirements of the inventivemethods, the inventive methods can be implemented in hardware orsoftware. The implementation can be performed using a digital storagemedium, in particular, a disk, a CD, a DVD or a Blu-ray disc, having anelectronically-readable control signals stored thereon, which cooperateswith a programmable computer system such that an embodiment of theinventive method is performed. Generally, an embodiment of the presentinvention is, therefore, a computer program product with a program codestored on a machine-readable carrier, the program code being operativefor performing the inventive method when the computer program productruns on a computer. In other words, embodiments of the inventive methodare, therefore, a computer program having a program code for performingat least one of the inventive methods when the computer program runs ona computer.

Aspects of the invention have been particularly shown and described withreference to particular embodiments thereof. It will be understood bythose skilled in the art that various other changes in the form anddetails may be made without departing from the spirit and scope thereof.It is, therefore, to be understood that various changes may be made inadapting the different embodiments without departing from the broaderconcept disclosed herein and comprehended by the claims that follow.

1. A sensor package, comprising: a printed circuit board that includes afirst main surface and a second main surface, wherein the second mainsurface is opposite to the first main surface; a laminar currentconductor arranged on the first main surface; a sensor chip arranged onthe second main surface and electrically insulated from the laminarcurrent conductor by the printed circuit board, wherein the sensor chipis adapted to measure a current flowing through the laminar currentconductor, and wherein the sensor chip comprises a magnetic fieldsensor; and wherein the sensor chip is hermetically sealed between amold material and the printed circuit board, or wherein the sensor chipis hermetically sealed within the printed circuit board.
 2. The sensorpackage of claim 1, wherein the magnetic field sensor is adapted toproduce a signal proportional to an intensity of the current flowingthrough the current conductor, and wherein the sensor package furthercomprises: an evaluation unit adapted to determine an output signal ofthe sensor chip representing a measure of the intensity of the currentflowing through the current conductor based on the signal of themagnetic field sensor and a calibration information.
 3. The sensorpackage of claim 2, wherein the calibration information accounts forposition tolerances between the current conductor and the magnetic fieldsensor.
 4. The sensor package according to claim 1, wherein the currentconductor comprises a first contact region, a second contact region anda magnetic field producing region electrically coupled between the firstand the second contact region.
 5. The sensor package according to claim4, wherein the magnetic field producing region has a vertical dimension,which is vertical relative to the first main surface of the printedcircuit board, and wherein the vertical dimension of the magnetic fieldproducing region is larger than a vertical distance between the magneticfield sensor and a surface of the current conductor facing the printedcircuit board.
 6. The sensor package according to claim 5, wherein thevertical dimension of the magnetic field producing region is more than1.5 times larger than the vertical distance between the magnetic fieldsensor and the surface of the current conductor.
 7. The sensor packageaccording to claim 5, wherein the vertical distance between the magneticfield sensor and the current conductor is larger than 50 μm and avertical dimension of the current conductor is larger than 100 μm. 8.The sensor package according to claim 5, wherein the current conductoris electrically insulated from the sensor chip by both: an insulatingarea of the printed circuit board arranged between the sensor chip andthe current conductor, and an additional insulating layer arrangedbetween the sensor chip and the current conductor.
 9. The sensor packageaccording to claim 4, wherein a maximum lateral dimension of themagnetic field producing region parallel to the first main surface ofthe printed circuit board and vertical to a main current flow directionof the magnetic field producing region is larger than a maximum verticaldimension of the magnetic field producing region vertical to the firstmain surface of the printed circuit board.
 10. The sensor packageaccording to claim 9, wherein the maximum lateral dimension of themagnetic field producing region is more than five times larger than themaximum vertical dimension of the magnetic field producing regionvertical to the first main surface of the printed circuit board.
 11. Thesensor package according to claim 4, wherein the sensor chip is adaptedto measure intensities of currents in a range of 20 A to 500 A, whereinan internal resistance of the first contact region, of the secondcontact region and of the magnetic field producing region is in a rangebetween 20μOhm to 3 mOhm, and wherein a lateral area of the magneticfield producing region is larger than a lateral area of a main surfaceof the sensor chip.
 12. The sensor package according to claim 4, whereinthe magnetic field producing region comprises at least one lateralnotch, and wherein the magnetic field sensor is arranged above thelateral notch and aligned to the lateral notch.
 13. The sensor packageof claim 1, wherein the sensor package further comprises: a discretecircuit element coupled between a pin of the sensor chip and an externalcontact of the sensor package, wherein the discrete circuit elementcomprises only material with a relative permeability of less than 1.1,or wherein the discrete circuit element is arranged spaced apart fromthe magnetic field sensor by at least 1.5 mm in case the discretecircuit element comprises material with a relative permeability of 1.1or more.
 14. The sensor package of claim 13, wherein the sensor packagedoes not comprise any discrete circuit element with a relativepermeability of more than 1.1 that is arranged in a distance smallerthan 1.5 mm to any magnetic field sensor element of the sensor chip. 15.The sensor package according to claim 13, wherein the discrete circuitelement is a capacitor, a fuse or a conductive lamination arranged onthe printed circuit board.
 16. The sensor package according to claim 1,wherein the sensor chip is at least partially embedded in the printedcircuit board.
 17. A sensor package, comprising: a printed circuit boardthat includes a first main surface and a second main surface, whereinthe second main surface is opposite to the first main surface; a laminarcurrent conductor arranged on the first main surface and adapted tocarry a current having a current intensity; a sensor chip arranged onthe second main surface and electrically insulated from the laminarcurrent conductor by the printed circuit board, wherein the sensor chipcomprises: a magnetic field sensor adapted to produce a signalproportional to the current intensity; and an evaluation unit adapted toevaluate the current intensity based on both the signal of the magneticfield sensor and individual calibration data, wherein the individualcalibration data is individual for individual sensor packages; andwherein the sensor chip is hermetically sealed between a mold materialand the printed circuit board, or wherein the sensor chip ishermetically sealed within the printed circuit board.
 18. The sensorpackage according to claim 17, wherein the laminar current conductorcomprises a first contact region, a second contact region and a magneticfield producing region electrically coupled between the first and thesecond contact region, and wherein a vertical dimension of the magneticfield producing region vertical to the first main surface of the printedcircuit board is larger than a vertical distance vertical to the firstmain surface of the printed circuit board between a surface of thecurrent conductor facing towards the sensor chip and the magnetic fieldsensor.